Electric fire-detector cable



April 3, 1956 F. G. KELLY ErAL 2,740,874

ELECTRIC FIRE-DETECTOR CABLE Filed Aug. l5, 1951 vi, Q

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l .B 1,00: v, @I E? '4' :inventors Il' 10o PMM jBober: posjcal 3H/H Bg reerl'clz lelllj lo LMA/ MW ma 20o soo 40o 50o 60o 7o TEMPERHTURE F. (www Unite States Patent Clifton, N. 3., cssignors to Thomas A. Edison, Incorporated, West 0r-ange, N. 3 a corporation of Nee7 Jersey Application August l5, 1951, Serial No. 241,992

17 Claims. (Ci. 201-63) This invention relates to an electrical device for detecting and/or measuring high temperatures, and more Vparticularly to a thermally-sensitive resistance device in the form of a cable for use as a re detector. The Vinvention is especially adapted for use in aircraft fire-detection equipment, but has other uses in temperature detection and/ or measurement equipment, as will be apparent.

lt is an object of our invention to provide an electrical resistance device which has a very high resistance at normal temperatures and such low resistance at higher temperatures as to enable control of a fire-detection signaling means without need for amplifying the control current.

lt is another object to obtain such low resistance at higher temperatures Vby a novel construction using electronic semiconductors without substantially any inert material.

Another object is to provide such semiconductors with an inert material to obtain higher-resistance operating characteristics.

t is another object to provide an electrical device, preferably in the form of a cable, which has uniform heat sensitivity throughout its length and which has a high negative temperature coetiicient of resistance,

lt is another object to provide a lire-detection cable of a rugged construction which can be bent on small radii and be subjected to severe vibration without undergoing any appreciable change in its operating characteristics.

It is another object to provide a heat-sensitive resistance device which has a highly stable operating characteristic in lower temperature ranges not exceeding 500 to l000 F. and which can be cycled through much higher ranges up to 2000" F. while retaining desired operating characteristics required in lire-detection equipment.

it is another object to provide improvements in therorally-sensitive resistance cables which enable them to be manufactured economically with uniform temperatureresistance characteristics.

it is another object to provide a practical and economical method of manufacturing cables of the character described.

ln particular, our invention resides in a thermallysensitive resistance cable which comprises a center wire, a spaced external conductive sheath and an intervening thermally-sensitive, electronic, oxygen-containing, semiconductive material, wherein the semiconductive material is caused to have a stable operating characteristic and a low resistive contact with the center wire and sheath, without the need for sintering the semiconductive material to the wire or sheath. Features of our invention by which these improved results are obtained reside in the proper selection of materials for the sheath and wire, in properly heat-treating the semiconductive material and in so constructing the cable that the semiconductive material at any given temperature will have substantially uniform oxygen concentration throughout the life of the cable. important steps in maintaining such constant and uniform oxygen concentration in the semiconductive material, after repeated cycling of the cable between hot and ice cold temperatures, are in compacting this material under such great pressure that air spaces therein are broken up and minimized, in subjecting vthe cable to la Slow firing temperature for a prolonged period while 'the cable is `in an inert atmosphere to equalize the oxygen pressure through the semiconductive .material and in then heattreating the cable to va high .firing temperature for afsuticient period to stabilize its characteristics and ,sets its calibration as will vbe apparent from the .following description.

These and `other objects and .features of our .invention will be apparent from the following kdescription and the appended claims.

ln the description of our invention reference is had to the accompanying drawings, of which:

Figure l is a fractional cross sectional view of a `*cable according to our invention taken through the central axis thereof;

Figure 2 is a transverse section taken on the line v2---2 of Figure 1;

Figure 3 is a typical curve of the resistance at room temperature vs. total time of heat treatment at a high tiring or stabilizing temperature for a cable using cobalt oxide for the semiconductor and constructed according to our invention; and

`Figure 4 shows typical curves of resistance vs. temperature for a finished cable using cobalt oxide and constructed according to our invention.

ln accordance with our invention we use one or more of the electron-defect semiconductive materials whose electronic conductivity at any given temperature increases with increase of oxygen pressure and concentration. This class of semiconductive materials includes oxides of cobalt, chrome, nickel, .manganese and copper.

The conductivity of these oxides at any given temperature substantially below their melting temperatures is dependent upon the amount of oxygen which they contain. Some of this oxygen is in the adsorbed state and the rest is in chemical combination. As the oxide is heated, some oxygen is driven off, according to the temperature and surrounding vapor pressure, to cause the electronic conductivity to increase. insofar as it is possible 'to -hold constant the amount of oxygen in the semiconductor at any given temperature, the cable will have stable operating characteristics.

Since the oxides abovementioned behave similarly under similar conditions, the same manufacturing procedure may be used for constructing cables using one or another, or combinations, of these oxides except for the temperatures at which the different heat-treating operations are carried out. 'These metal oxides do, however, have different specic resistivities, different sharpness of response to temperature change, and different melting temperatures, to require selection of specific oxides for particular applications. Of the several oxide materials mentioned, that of cobalt is particularly desirable for use in aircraft lire-detection equipment because it has a relatively low specic resistivity, a high temperature sensitivity of the order of a 50% decrease in resistance for each 27 F. increase in temperature, and a melting temperature well above 2000 F. By way of preferred illustration, we do particularly describe `our invention in connection with cobalt oxide as the semiconductive material, but it will be understood that we intend no unnecessary limitation of our invention to this material.

The construction of thermally-sensitive resistance cables using one or more of the metal oxides abovementioned must be carried out by a special manufacturing procedure under uniform conditions in order that the cables will have uniformly the desired operating characteristics. This is important because the materials used, the method of assembling the cable and the heat-treating steps car- `ried out before sealing the cable are all vital in establishing the oxygen concentration of the semiconductive material and the final operating characteristics of the cable. Our invention resides therefore not only in the finished product but also in the method of manufacture thereof, as will be apparent.

The fire-detector cable shown in the accompanying figures comprises a central metal wire llt) constituting one electrode of the cable, a spaced'metal protective sheath 11 constituting a second electrode, and an intervening semiconductive material of cobalt oxide l2. This cobalt oxide is provided continuously along the length of the cable and is the sole means which holds the wire 10 centralized in relation to the sheath except for the use of a ceramic bead 13 at each end of the cable. The semiconductor can in our invention be so utilized as the sole spacing means since the class of semiconductors abovementioned remain in the solid state throughout their operating range.

The ends of the cable are sealed airtight to prevent ingress of moisture and change of the oxygen content of i the cobalt oxide. This sealing is done by means of hermetic seals 14 each comprising a glass bead 15 fuzed to outer and inner tubing sections 16 and 17. These tubing sections are telescoped onto the sheath and wire respectively and the ends thereof are secured airtight to the sheath to be reduced in diameter to effect a high compres- 5 sion of the cobalt oxide in the manufacturing of the cable, as will appear. We have found that a nickel-iron alloy, preferably of 42% nickel and the remainder iron, has these desired characteristics.

Such nickel-iron alloy is also very suitable for the core k of the center wire 10. However, because this wire has small surface area relative to that of the surrounding sheath, an exceptionally good mechanical bond of low electrical resistance is required between the Wire and the cobalt oxide. To obtain this bond, the nickel-iron wire is copper-clad. Such copper-clad nickel-iron wire is known commercially as Dumet wire. The copper covering on this wire serves several functions in obtaining a good mechanical and electrical bond. Firstly, as the cable is heat-treated in the fabrication thereof, the copper covering oxidizes and is bonded tenaciously both to the cobalt oxide and to the nickel-iron core of the wire. Secondly, the copper oxide which is so formed is an excellent electrical conductor providing a low-resistance electrical connection between the cobalt oxide and the nickel-iron core. Thirdly, the copper oxide seals of the nickel-iron core from the enclosed atmosphere to prevent oxidation of the core. This is very important since nickel-iron oxide has relatively high electrical resistance.

In order to obtain a high degree of stability in the operating characteristics of the cobalt oxide, we have found that it is important that the oxide be tired in the open air before it is introduced into the sheath in order to establish its oxygen concentration, that it be compressed so tightly in the sheath as to preclude any substantial diffusion of oxygen through it, that the cable be next heated uniformly in an inert atmosphere to a low tiring temperature of the order of l100 F. for a prolonged period for the purpose of equalizing the oxygen pressure throughout the cobalt oxide, and that finally the cable be heated to an orange-yellow firing temperature of the order of 1800 F. for such length of time as will stabilize its operating characteristics and set its calibration at the desired value, as is herein later described. The processing steps by which these and other desired objectives are ob- 4 tained in the manufacture of the present cable are carried out preferably in the manner herein next described,

Firstly, the cobalt oxide is micropulverized until the powdered material will pass through a S25-mesh screen. An inorganic lubricant and binder known as Veegum is then ground to pass a S25-mesh screen. This Veegum is a magnesium aluminum silicate which in its typical commercial form comprises 61.1% silicon dioxide, 13.7% magnesium oxide, 9.3% aluminum oxide, .1% titanium dioxide, .9% ferric oxide, 2.7% calcium oxide, 2.9% sodium oxide, .3% potassium oxide, 1.8% carbon dioxide and 7.2% water. About 4% of the Veegum by weight of cobalt oxide is added to the latter and the two are then mixed uniformly. The Veegum is a lubricant needed to enable the cobalt oxide to be extruded onto the center wire in the manner` herein later described. The `Veegum remains in the cobalt oxide as an inert material but has no deleterious effects.

The present cable uses no other inert materials in the semiconductor than the Veegum abovementioned in order that the cable will have a very low resistance at the operating temperature at which it is to trip an alarm. For instance, as will appear, a cable using substantially pure semiconductive material may have a resistance of only 100 ohms or less at an operating temperature of 300 to 400 F. If a higher resistance is desired at such operating temperature, or the same resistance is desired at a higher operating temperature, any suitable inert material may be added to the semiconductor.

Before the mixture of cobalt oxide and Veegum is extruded onto the wire, it is moistened with approximately 10% of water by Weight of the mix. This water is added gradually while the mix is stirred to get an even composition. The water serves to plasticize the mix to facilitate the extrusion operation aforementioned.

The plasticized mix of cobalt oxide, Veegum and water is next extruded onto the center wire 1t) by a standard extruding apparatus for such purpose, the diameter of the extrusion being such that it can be inserted easily into the sheath il. in order that the extruded material will have suiicient frictional contact with the wire to carry the wire along without slippage, the surface of the Wire is first sanded or otherwise roughened or scored. If the mix is properly plasticized, and the wire is straight and suitably scored, the extrusion on the wire will be smooth and uniform in diameter. Moreover, this extrusion will have a fair mechanical strength and adherence to the wire to enable handling thereof in the next manufacturing step without the extruded material breaking loose from the wire.

Before the center wire with the extrusion covering is inserted into the sheath 11, it is air dried for about 24 hours in a clean, dry room. Thereafter, it is heated in air to an orange-yellow firing temperature of the order of l800 F. for about 5 minutes, the length of time of this firing being however not critical. This firing operation is carried out suitably in an electrically-heated oven so as to effect uniform heating, a uniform heating being important in order that the final cable will have uniform characteristics along its length. In this firing operation the Water content in the mix is completely driven off and the oxygen concentration in the cobalt oxide is established. Since the concentration of oxygen in the air is constant, a firing of any number of the extrusions in air at the same temperature for the same length of time, and otherwise under the same conditions, will result in each extrusion having the same oxygen concentration. it is important therefore that this tiring operation be carried out under uniform conditions.

After the center wire with the extrusion covering is inserted into the sheath, the latter is reduced to about half of its original diameter. This reduction may be effected by successive drawing operations, as by pulling the sheath through successive reducing dies, and is otherwise done by means of a swaging machine, in which case :the reduction can be carried out in one operation.

'pacting This compacting is important in the manufacture of the present cable since it assures a strong, uniform mechanical and electrical contact between the sheath, the cobalt oxide and the wire and, further, since it eliminates essentially all free air paths in the cobalt oxide itself as well as between the cobalt oxide and the sheath and wire to stabilize the operating characteristics of the cable. For instance, if such air paths were allowed to exist, the oxygen would be forced to cooler portions of `the cable as the cable is heated, and when the cable is next cooled, those portions of the cable from which the oxygen escaped would have a much higher resistance. This would cause a change in the operating characteristics of the cable as a Whole, and would in particular cause the cable to have non-uniform characteristics along its length. On the other hand, when the cobalt oxide is compacted as above described, the wall of the sheath is so adherent to the cobalt oxide, and the oxide is so compressed, that the oxygen which escapes from elemental portions of the cobalt oxide as the cable is heated is localized in tiny, sealed air pockets adjacent to those portions. Upon cooling the cable, the localized oxygen is recombined with the adjacent cobalt oxide elemental portions to cause the cobalt oxide to have again its original oxygen concentration and therefore its original specific resistivity throughout the length of the cable.

As a further step in obtaining greater uniformity in the operating characteristics of the cables throughout their lengths, each cable, after being reduced in diameter as just described, is heated in an inert atmosphere, as by means of an oven, to a low Vdull-red tiring temperature of the order of ll F. for a prolonged period of the order of 48 to 72 hours. ln this heat treatment, oxygen is liberated and gradually diffused through the oxide to equalize the oxygen pressure in all portions of the cable. When the cable `is next cooled to room temperature, the Voxygen concentration of all portions of the cobalt oxide `is fairly uniform.

At the completion of the foregoing heat treatment to `equalize the oxygen pressure, each cable is subjected to a iinal heat treatment to set its calibration at the desired value, and then the cable is hermetically sealed to cornplete the same. The final heat treatment is carried out by subjecting the cable, before it is hermetically sealed, to a high orange-yellow ring temperature of the order of l800 F. in an inert atmosphere as of nitrogen and hydrogen. The length of time that the cable is so heated determines its calibration-i. e., the resistance of the cable at a given operate temperature. For instance, a cable using cobalt oxide and having a sheath of .080l outside diameter and .012 wall thickness, a center wire of .025 diameter, and an overall length of has a characteristic of room temperature resistance vs. tiring time approximately as shown by curve A of Figure 3. This characteristic is obtained by heating the cable in successive steps, cooling it to room temperature and measuring its resistance after each successive step, and plotting that resistance against the respective total firing time. The curve A is shown in terms of the resistance atroom temperature because the cable has no measurable resistance at the firing temperature.

It will be noted that curve A of Figure 3 has a hump in the heating period range between 3 minutes and l0 minutes total ring time, representing an unstable portion of the characteristic. To avoid this unstable portion of the characteristic the cable should be heated at the ring temperature for a period of at least l0 minutes. For heating periods greater than l0 minutes, the room temperature resistance increases very gradually with increased heating time, and reaches an asymptote at a resistance value which typically is several times greater than the minimum resistance value beyond the hump.

5 This gradual rise in room temperature resistance with increased heating time at the firing temperature is due to oxygen being gradually lost from the semiconductor and being combined with the exposed surfaces of the sheath and wire at this temperature. As oxygen is lost from the semiconductor, the resistance of the latter increases; also, as such oxygen combines with the sheath and center wire elements, the resistance of the oxidized layers between the cobalt oxide and these elements may also increase. However, as the surfaces of the sheath and wire become more and more oxidized, further oxidation is retarded to cause the room temperature resistance to approach an asymptote and the cable to approach a fixed operating characteristic.

From the foregoing explanation it will be apparent that the cable can be calibrated to have a preselected value of room temperature resistance on the stabilized portion of the characteristic curve A between the minimum value abovernentioned and the asymptote by choosing the proper period of heating of the cable at the tiring temperature. If a room temperature resistance greater than the asymptotic value is desired, an inert material such as magnesium oxide is added to the cobalt oxide.

The variation in resistance with change in temperature of the nished cable whose heat-treatment characteristic is shown in Figure 3, is shown approximately by the resistance vs. temperature curves B and C of Figure 4, the characteristic B being for a cable having a room temperature resistance of the order of 33,000 ohms, which is the minimum room temperature resistance beyond the hump on the curve A of Figure 3, and the characteristic curve C being for a cable having a room temperature resistance of the order of 470,000 ohms, such latter cable being realizable by the use of an inert mate` rial in the semiconductor as above mentioned. These characteristics are approximately parallel when the resistance is plotted to a logarithmic scale as shown. Because of this parallelism, it follows that when any one characteristic is known for a particular semiconductor, the resistance at a given operating temperature can be readily found graphically for a body of that semiconductor having a known room temperature resistance. Likewise, in a reverse sense, if an operate resistance is preselected at some prescribed operate temperature, the required room temperature resistance of the cable can be readily found. Thus, with the aid of curve A of Figure 3, and of curve B or C of Figure 4, the approximate heat-treatincr time can be predetermined for a cable that is to have a given resistance at a prescribed operate time.

When a finished cable is cycled through a temperature range, its resistance temperature characteristic illustrated in Figure 4 will shift only insofar as oxygen is 10st permanently from the semiconductor and is combined with the sheath and center wire. Cycling a finished cable between room temperature and only a moderately-high temparato-re of the order of 1000 F. or less will not cause any appreciable loss in oxygen and will not change substantially the characteristic of the cable. Within such lower range, the cable is suitable for temperature-measuring purposes. Cycling of the cable between room temperature and a higher temperature of the order of l800 F. will cause a gradual shift in the room temperature resistance of the cable to the extent of the total time of such heating, as shown by curve A, with a resultant similar change in the operate temperature resistance of the cable. T his shift is, however, so gradual that a cable can be cycled a number of times between these temperatures without the operating characteristic shifting beyond required limitations for aircraft lire-detection equipment.

lt is desirable that aircraft lire-detection equipment shall alarm at operate temperatures of the order of 250 to 500 F., or at least at tempertaures no greater than l000 F. lt is also important that the fire-detection element of such equipment have a high resistance at normal temperatures and a low resistance of the order of only l() ohms at the prescribed operate temperature. The importance of a low operate resistance is that under aircraft environmental conditions carbonized oil, water and dirt will form on the detection element and may bridge the terminals thereof to produce shunt paths having resistances as low as 1000 ohms. A lire-detecting element that does not have a resistance at the prescribed operate temperature which is considerably below 1G00 ohms will therefore give false alarms.

As far as is known, no fire-detection cable using semiconductors has been heretofore produced which has operate temperature resistances even as low as 100() ohms. By the present invention, however, operate resistances of only l0() ohms are readily obtainable. For instance, the characteristic B of Figure 4 shows that an operate resistance of i) ohms is obtained at only 290 F. with a cable having a room temperature resistance of 33,060 ohms. if it is desirable that the cable have a higher room temperature resistance, say a resistance of the order of 430,060 ohms, which higher resistance cable is obtainable by adding inert material to the semiconductor as aforementioned, the operate resistance of l0() ohms is obtained at a temperature of 400 F. as shown by characteristic C of Figure 4. The ability to produce cables having such low operate resistances which have yet a very high room temperature resistance represents a marked advance in the lire-detection iield since it means that false alarms can be well-nigh positively precluded not only because such operate resistance is substantially lower than the shunt paths that tend to form from carbonized oil, water, etc., but also because such low operate resistances enable the use of very simple control apparatus operable directly by the control current without need for ampliiication.

The foregoing specic description of our invention in terms of cobalt oxide as the semiconductive material is illustrative of the use of other such materials of the electron-defect type since all of these materials behave similarly except as to their temperature ranges. Such and other modifications in the speciiic embodiment of our invention herein particularly described will be apparent to those skilled in the art and are comprehended within the scope of our invention, which we endeavor to set forth in the following claims.

We claim:

l. A resistance-type temperature-responsive cable comprising a tubular sheath of a ductile nickel-iron alloy, a copper-clad nickel-iron wire at the center of said sheath lengthwise thereof, substantially pure electronic semiconductive oxygen containing compound tending to release oxygen and to recombine therewith with change in its resistivity as the compound is heated and cooled through a temperature range below its melting point, said compound filling the space between said sheath and wire and constituting a means for holding said wire centered in relation to said sheath along the length of the cable, said sheath being constricted tightly onto said compound and being hermetically sealed, and said sheath and wire having oxidized surfaces contacting said compound to cause the oxygen pressure in said sheath to return to substantially the same value after each cycling of the cable to a iiring temperature and cooling thereof to room temperature.

2. The temperature-responsive device set forth in claim 13 wherein said semiconductive material is cobalt oxide and said conductors are nickel-iron alloys having substantially the same thermal coeiiicient of expansion as that of said cobalt oxide.

3. The method of producing a resistance-type temperature-responsive cable which comprises forming a uniform covering of electronic oxide semiconductive material on a metal wire, tiring said covered wire in the atmosphere at a predetermined temperature to establish the oxygen concentration in said material, inserting said covered Wire in a metal sheath, constricting the diameter of said sheath to compact said material tightly whereby to break up air spaces therein and to form low-resistance electrical connections between said semiconductive material and said wire and sheath respectively, heating said cable at a low dull-red firing temperature to equalize the oxygen pressure in said semiconductive material, and heating said cable next to a high orange-yellow iiring temperature to stabilize the operating characteristics of said cable.

d. The method of producing a resistance-type temperature-responsive cable which comprises forming a uniform covering of electronic oxygen containing semiconductive material on a metal wire, firing said covered wire in a predetermined atmosphere at a predetermined temperature, inserting said covered wire in a metal sheath, constricting the diameter of said sheath to compact said material tightly whereby to break up air spaces therein, heating said cable in an inert atmosphere to an orange-yellow firing temperature for a predetermined length of time for stabilizing the operating characteristics of the cable and setting its calibration, and hermetcally sealing the ends of said cable.

5. The method of producing a resistance-type temperature-responsive cable which comprises forming a uniform covering of electronic oxide semiconductive material on a metal wire, tiring said covered wire in the atmosphere at a predetermined temperature to establish the oxygen concentration in said material, inserting said covered wire in a metal sheath, constricting the diameter of said sheath to compact said material tightly whereby to break up air spaces therein, heating said cable in an inert atmosphere at a low dull-red tiring temperature for a prolonged period to equalize the oxygen pressure in said semiconductive material, and heating said cable next to a higher, orange-yellow tiring temperature in an inert atmosphere for a period suliicient to stabilize the operating characteristics of the cable.

6. The method of stabilizing the electrical characteristics of a resistance-type temperature-responsive metalsheathed cable using an electronic oxygen containing type semiconductive material, which comprises reducing the diameter of the sheath of the cable to compact tightly said semiconductive material and to eliminate essentially all air paths therein, heating .said cable for a prolonged period to a low, dull-red, firing temperature to equalize the oxygen pressure of said material, and heating said cable to a high, orange-yellow, ring temperature for a length of time sufficient to stabilize its characteristics and to set the calibration of the cable to a preselected point.

7. The method of constructing a resistance-type temperature-responsive cable having a preestablished resistance for a given temperature, comprising inserting a center wire and surrounding filling material in a metal sheath having an internal surface material capable of undergoing oxidation when heated to a tiring temperature in an oxidizing atmosphere, said lling material comprising an electronic thermally responsive oxygencontaining semiconductor tending to release oxygen as gas when heated and to recombine with available oxygen when cooled, said semiconductor having a resistivity which at a given temperature varies according to the amount of oxygen contained in chemical combination, said conductor containing initially a predetermined excess of oxygen concentration, and heating said cable to release oxygen from said filling material and to cause chemical combination thereof with said internal surface material.

8. The method of constructing a resistance-type temperature-responsive cable having a preestablished resistance for a given temperature, comprising inserting a center wire and lling material in a metal sheath having an internal surface material capable of undergoing oxidation when heated to a tiring temperature in an oxidizing atmosphere, said filling material comprising an electronic oxygen containing semiconductor tending to manently released from said semiconductor and to be combined with said internal surface material.

9. The method of producing a resistance-type temperature-responsiv'e cable which comprises forming on a metal wire a uniform covering of electronic oxygen containing semiconductive material, inserting said covered Wire into a metal sheath, constricting the diameter of said sheath to compact said material to minimize gas pockets therein and to form low-resistance electrical connections between said material and said wire and sheath respectively, and heating said cable to a high orange-yellow firing temperature for a predetermined length of time adapted to set the resistance of the cable at a predetermined value and to stabilize its operating characteristics.

10. A resistance-type temperature-responsive cable of indefinite length comprising a metal sheath, a central wire extending throughout the length of said sheath, finely pulverized material comprising an electronic semiconductor, of the electron-defect type and containing substantially no ionic conductive material, said material filling the space between said sheath and central conductor, said semiconductor being of a type having a resistivity which varies as the temperature of the semiconductor is varied from a reference value and said semiconductor having the property when cooled from a heated state of combining with available oxygen with resultant change in its reference resistivity, said filling material being under compression by said sheath to form stable low-resistance electrical connections between said semiconductor and said wire and sheath respectively, and said sheath having an oxidation-resistant internal surface and being sealed at the ends without entrapment of any gas space therewithin.

ll. A resistance-type temperature-responsive cable of indefinite length comprising a gas-impervious metal sheath, a central conductor extending throughout the length of said sheath, finely pulverized material comprising au electronic semiconductor and substantially no ionic conductive material, said pulverized material filling the space between said sheath and central conductor, said semiconductor being of an electron-defect type containing oxygen in chemical combination and having a thermally responsive resistivity which at a given temperature varies according to the amount of oxygen so contained, and said semiconductor tending to release oxygen in gaseous state as the semiconductor is heated into a temperature region below its melting point and tending to recombine therewith as the semiconductor is cooled, said sheatth having an inner surface layer contacting said filling material and substantially inert to oxidation throughout the opening temperature range of said cable, means sealing the ends of said cable without entrapment of air space therewithin, and said filling material being consolidated in said sheath to preclude gaseous diffusion therethrough with resultant confinement of oxygen in intimate contact with the portion of the semiconductor from which it is released when the cable is heated whereby substantially total recombination of said portions occurs as the cable is cooled.

l2. A resistance-type temperature-responsive cable of continuous indefinite length adapted for operation in a prescribed temperature range and comprising a gas-impervious ductile metal sheath having internal oxidizable Vsurface material, a Center wire in said sheath, temperature-responsive material filling the space between said sheath and center wire and comprising at least predominantly an electronic oxidic semiconductor having a resistivity depending yon its oxygen concentration and tending to release oxygen gas when heated above a predetermined temperature and to recombine with said released gas to extent 'available when cooled, said sheath being constricted onto said temperature-responsive material to consolidate the material in the sheath under pressure, and said intern-al surface material of said sheath being oxidized by oxygen from said semiconductor released by heating .said cable at temperatures above said prescribed operating temperature range.

13. A resistance-type temperature-responsive device of indelinite continuous length comprising a Vwire conductor of oxidizable metal, a covering of temperature-responsive resistance material on said wire conductor, a tubular conductor of oxidizable metal surrounding said covered wire conductor and constricted along its length to a reduced diameter thereonto to compress said temperature-responsive material into a solid non-porous state substantially impervious to gaseous diffusion along its length, said temperature-responsive material comprising predominantly an electronic oxidic semiconductor, and said material being sintered in said tubular conductor and being bonded intimately to the surfaces of said conductors by oxidation of said surfaces by oxygen from the electronic semiconductor during the sintering operation.

14. A resistance-type temperature-responsive device of indefinite continuous length adapted for operation through a prescribed temperature range, comprising a tubular conductor of oxidizable metal, a wire conductor of oxidizable metal inserted in said tubular conductor and spaced from its walls, a temperature-responsive resistance material compacted into the space between said conductors into an essentially solid non-porous state impervious to gaseous diffusion along its length, said material being substantially free of ionic conductive material and comprising predominantly an electronic oxidic semiconductor havinv a resistivity at any temperature below its melting point dependent on the amount of oxygen which it contains, said tubular conductor being hermetically sealed without entrapment of any air space therewithin, and said material being sintered in said tubular conductor to bond the material to the surfaces of said conductors by oxidation of said surfaces by oxygen from the semiconductor during the sintering operation.

l5. A resistance-type temperature-responsive device of indefinite continuous length comprising a metal wire conductor, a covering of temperature-responsive resistance material on said wire conductor, a tubular conductor surrounding said covered wire conductor, said tubular conductor being constricted along its length to a reduced diameter to compress said temperature-responsive material and said material being sintered whereby to form it into a solid coherent mass substantially impervious to gaseous diusion and having intimate electrical contact with the surfaces of said conductors, said temperatureresponsive material containing substantially no ionic conductive material and comprising predominantly an electronic oxidic semiconductor.

16. A flexible resistance-type temperature-responsive cable comprising an exterior tubular sheath, an axiallypositioned center wire extending lengthwise of said sheath, and a substantially pure electronic semiconductive material having a negative temperature coeicient of resistance and compacted in the space between said sheath and wire, said semiconductive material constituting the sole medium along the length of said cable for holding said wire centered in relation to said sheath, wherein said center wire comprises a metal alloy core clad with copper, and wherein said copper is converted at least partially to copper oxide to bond said semiconductive material to said metal alloy core.

andere 17. A flexible resistance-type temperature-responsive cable comprising an exterior tubular sheath, an axiallypositioned center wire extending lengthwise of said sheath, and a substantially pure electronic semiconductive material having a negative temperature coecient of resistance and compacted in the space between said sheath and Wire, said semiconductive material constituting the sole medium along Jthe length of said cable for holding said Wire centered in relation to said sheath, said semiconductive material being of an electron-defect type comprising oxygen in chemical composition and having a thermally-responsive resistivity which at a given temperature varies according to the amount of oxygen so contained, said serni conductive material tending to release oxygen as gas and to recombine with available oxygen in intimate contact therewith respectively as the semiconductive material is heated and cooled through a temperature range below its melting point, the mass of said semiconductive material being free of open space to conne the oxygen gas in intimate contact with the portions of the semiconductive material from which it escapes While the semiconductive material is heated, and said cable being hermetieally sealedwithout entrapment of air space therewithin.

References Cited in the ile of this patent UNITED STATES PATENTS 2,216,375 Minter Oct. 1, 1940 2,271,975 Hall Feb. 3, 1942 2,414,793 Becker et al. Ian. 28, 1947 2,477,348 Postal July 26, 1949 2,495,867 Peters Ian. 31, 1950 2,594,921 Hansard Apr. 29, 1952 

9. A RESISTANCE-TYPE TEMPERATURE-RESPONSIVE CABLE COMPRISING A TUBULAR SHEATH OF A DUCILE NICKEL-IRON ALLOY, A COPPER-CLAD NICKEL-IRON WIRE AT THE CENTER OF SAID SHEATH LENGHTWISE THEREOF, SUBSTANTIALLY PURE ELECTRONIC SEMICONDUCTIVE OXYGEN CONTAINING COMPOUND TENDING TO RELEASE OXYGEN AND TO RECOMBINE THEREWITH WITH CHANGE IN ITS RESISTIVITY AS THE COMPOUND IS HEATED AND COOLED THROUGH A TEMPERATURE RANGE BELOW ITS MELTING POINT, SAID COMPOUND FILLING THE SPACE BETWEEN SAID SHEATH AND WIRE AND CONSTITUTING A MEANS FOR HOLDING SAID WIRE CENTERED IN RELATION TO SAID SHEATH ALONG THE LENGTH OF THE CABLE, SAID SHEATH BEING CONSTRICTED TIGHTLY ONTO SAID COMPOUND AND BEING HERMETICALLY SEALED, AND SAID SHEATH AND WIRE HAVING OXIDIZED SURFACE CONTACTING SAID COMPOUND TO CAUSING THE OXYGEN PRESSURE IN SAID SHEATH TO RETURN TO SUBSTANTIALY THE SAME VALUE AFER EACH CYCLING OF THE CABLE TO A FIRING TEMPERATURE AND COOLING THEREOF TO ROOM TEMPERATURE. 